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data-v-6b87e69f><!--[--><!--]--><!----><main class="main" data-v-6b87e69f><div style="position:relative;" class="vp-doc _largeFrontEnd_flutter_chapter6_custom_scrollview" data-v-6b87e69f><div><h1 id="_6-10-customscrollview-和-slivers" tabindex="-1">6.10 CustomScrollView 和 Slivers <a class="header-anchor" href="#_6-10-customscrollview-和-slivers" aria-label="Permalink to &quot;6.10 CustomScrollView 和 Slivers&quot;">​</a></h1><h2 id="_6-10-1-customscrollview" tabindex="-1">6.10.1 CustomScrollView <a class="header-anchor" href="#_6-10-1-customscrollview" aria-label="Permalink to &quot;6.10.1 CustomScrollView&quot;">​</a></h2><p>前面介绍的 ListView、GridView、PageView 都是一个<strong>完整</strong>的可滚动组件，所谓完整是指它们都包括Scrollable 、 Viewport 和 Sliver。假如我们想要在一个页面中，同时包含多个可滚动组件，且使它们的滑动效果能统一起来，比如：我们想将已有的两个沿垂直方向滚动的 ListView 成一个 ListView ，这样在第一ListView 滑动到底部时能自动接上第二 ListView，如果尝试写一个 demo：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildTwoListView</span><span style="color:#E1E4E8;">() {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">var</span><span style="color:#E1E4E8;"> listView </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">ListView</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">builder</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      itemCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">20</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">      itemBuilder</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> (_, index) </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">ListTile</span><span style="color:#E1E4E8;">(title</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;$</span><span style="color:#79B8FF;">index</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">)),</span></span>
<span class="line"><span style="color:#E1E4E8;">    );</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Column</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      children</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> [</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#79B8FF;">Expanded</span><span style="color:#E1E4E8;">(child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> listView),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#79B8FF;">Divider</span><span style="color:#E1E4E8;">(color</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Colors</span><span style="color:#E1E4E8;">.grey),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#79B8FF;">Expanded</span><span style="color:#E1E4E8;">(child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> listView),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ],</span></span>
<span class="line"><span style="color:#E1E4E8;">    );</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"><span style="color:#E1E4E8;">}</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildTwoListView</span><span style="color:#24292E;">() {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">var</span><span style="color:#24292E;"> listView </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">ListView</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">builder</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      itemCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">20</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">      itemBuilder</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> (_, index) </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">ListTile</span><span style="color:#24292E;">(title</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;$</span><span style="color:#005CC5;">index</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">)),</span></span>
<span class="line"><span style="color:#24292E;">    );</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Column</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      children</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> [</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#005CC5;">Expanded</span><span style="color:#24292E;">(child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> listView),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#005CC5;">Divider</span><span style="color:#24292E;">(color</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Colors</span><span style="color:#24292E;">.grey),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#005CC5;">Expanded</span><span style="color:#24292E;">(child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> listView),</span></span>
<span class="line"><span style="color:#24292E;">      ],</span></span>
<span class="line"><span style="color:#24292E;">    );</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"><span style="color:#24292E;">}</span></span></code></pre></div><p>运行效果如图6-22所示：</p><p><img src="/assets/6-22.bd42e676.gif" alt="图6-22"></p><p>页面中有两个 ListView，各占可视区域一半高度，虽然能够显式出来，但每一个 ListView 只会响应自己可视区域中滑动，实现不了我们想要的效果。之所以会这样的原因是两个 ListView 都有自己独立的 Scrollable 、 Viewport 和 Sliver，既然如此，我们自己创建一个共用的 Scrollable 和 Viewport 对象，然后再将两个 ListView 对应的 Sliver 添加到这个共用的 Viewport 对象中就可以实现我们想要的效果了。如果这个工作让开发者自己来做无疑是比较麻烦的，因此 Flutter 提供了一个 <code>CustomScrollView</code> 组件来帮助我们创建一个公共的 Scrollable 和 Viewport ，然后它的 slivers 参数接受一个 Sliver 数组，这样我们就可以使用CustomScrollView 方面的实现我们期望的功能了：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildTwoSliverList</span><span style="color:#E1E4E8;">() {</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// SliverFixedExtentList 是一个 Sliver，它可以生成高度相同的列表项。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 再次提醒，如果列表项高度相同，我们应该优先使用SliverFixedExtentList </span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 和 SliverPrototypeExtentList，如果不同，使用 SliverList.</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">var</span><span style="color:#E1E4E8;"> listView </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverFixedExtentList</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">    itemExtent</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">56</span><span style="color:#E1E4E8;">, </span><span style="color:#6A737D;">//列表项高度固定</span></span>
<span class="line"><span style="color:#E1E4E8;">    delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverChildBuilderDelegate</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      (_, index) </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">ListTile</span><span style="color:#E1E4E8;">(title</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;$</span><span style="color:#79B8FF;">index</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">)),</span></span>
<span class="line"><span style="color:#E1E4E8;">      childCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">10</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">    ),</span></span>
<span class="line"><span style="color:#E1E4E8;">  );</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 使用</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">CustomScrollView</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">    slivers</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> [</span></span>
<span class="line"><span style="color:#E1E4E8;">      listView,</span></span>
<span class="line"><span style="color:#E1E4E8;">      listView,</span></span>
<span class="line"><span style="color:#E1E4E8;">    ],</span></span>
<span class="line"><span style="color:#E1E4E8;">  );</span></span>
<span class="line"><span style="color:#E1E4E8;">}</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildTwoSliverList</span><span style="color:#24292E;">() {</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// SliverFixedExtentList 是一个 Sliver，它可以生成高度相同的列表项。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 再次提醒，如果列表项高度相同，我们应该优先使用SliverFixedExtentList </span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 和 SliverPrototypeExtentList，如果不同，使用 SliverList.</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">var</span><span style="color:#24292E;"> listView </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverFixedExtentList</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">    itemExtent</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">56</span><span style="color:#24292E;">, </span><span style="color:#6A737D;">//列表项高度固定</span></span>
<span class="line"><span style="color:#24292E;">    delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverChildBuilderDelegate</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      (_, index) </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">ListTile</span><span style="color:#24292E;">(title</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;$</span><span style="color:#005CC5;">index</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">)),</span></span>
<span class="line"><span style="color:#24292E;">      childCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">10</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">    ),</span></span>
<span class="line"><span style="color:#24292E;">  );</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 使用</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">CustomScrollView</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">    slivers</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> [</span></span>
<span class="line"><span style="color:#24292E;">      listView,</span></span>
<span class="line"><span style="color:#24292E;">      listView,</span></span>
<span class="line"><span style="color:#24292E;">    ],</span></span>
<span class="line"><span style="color:#24292E;">  );</span></span>
<span class="line"><span style="color:#24292E;">}</span></span></code></pre></div><p>运行后效果图6-23所示：</p><p><img src="/assets/6-23.befc09b3.gif" alt="图6-23"></p><p>可以看到我们期望的效果实现了。</p><p>综上，<code>CustomScrollView</code> 的主要功能是提供一个公共的 Scrollable 和 Viewport，来组合多个 Sliver，CustomScrollView 的结构如图6-24：</p><p><img src="/assets/6-24.b963924e.png" alt="图6-24"></p><h2 id="_6-10-2-flutter-中常用的-sliver" tabindex="-1">6.10.2 Flutter 中常用的 Sliver <a class="header-anchor" href="#_6-10-2-flutter-中常用的-sliver" aria-label="Permalink to &quot;6.10.2 Flutter 中常用的 Sliver&quot;">​</a></h2><p>之前小节介绍过的可滚动组件都有对应的 Sliver：</p><table><thead><tr><th>Sliver名称</th><th>功能</th><th>对应的可滚动组件</th></tr></thead><tbody><tr><td>SliverList</td><td>列表</td><td>ListView</td></tr><tr><td>SliverFixedExtentList</td><td>高度固定的列表</td><td>ListView，指定<code>itemExtent</code>时</td></tr><tr><td>SliverAnimatedList</td><td>添加/删除列表项可以执行动画</td><td>AnimatedList</td></tr><tr><td>SliverGrid</td><td>网格</td><td>GridView</td></tr><tr><td>SliverPrototypeExtentList</td><td>根据原型生成高度固定的列表</td><td>ListView，指定<code>prototypeItem</code> 时</td></tr><tr><td>SliverFillViewport</td><td>包含多个子组件，每个都可以填满屏幕</td><td>PageView</td></tr></tbody></table><p>除了和列表对应的 Sliver 之外还有一些用于对 Sliver 进行布局、装饰的组件，<strong>它们的子组件必须是 Sliver</strong>，我们列举几个常用的：</p><table><thead><tr><th>Sliver名称</th><th>对应 RenderBox</th></tr></thead><tbody><tr><td>SliverPadding</td><td>Padding</td></tr><tr><td>SliverVisibility、SliverOpacity</td><td>Visibility、Opacity</td></tr><tr><td>SliverFadeTransition</td><td>FadeTransition</td></tr><tr><td>SliverLayoutBuilder</td><td>LayoutBuilder</td></tr></tbody></table><p>还有一些其他常用的 Sliver：</p><table><thead><tr><th>Sliver名称</th><th>说明</th></tr></thead><tbody><tr><td>SliverAppBar</td><td>对应 AppBar，主要是为了在 CustomScrollView 中使用。</td></tr><tr><td>SliverToBoxAdapter</td><td>一个适配器，可以将 RenderBox 适配为 Sliver，后面介绍。</td></tr><tr><td>SliverPersistentHeader</td><td>滑动到顶部时可以固定住，后面介绍。</td></tr></tbody></table><blockquote><p>Sliver系列 Widget 比较多，我们不会一一介绍，读者只需记住它的特点，需要时再去查看文档即可。上面之所以说“大多数”Sliver都和可滚动组件对应，是由于还有一些如SliverPadding、SliverAppBar 等是和可滚动组件无关的，它们主要是为了结合CustomScrollView一起使用，这是因为<strong>CustomScrollView的子组件必须都是Sliver</strong>。</p></blockquote><h3 id="示例" tabindex="-1">示例 <a class="header-anchor" href="#示例" aria-label="Permalink to &quot;示例&quot;">​</a></h3><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#6A737D;">// 因为本路由没有使用 Scaffold，为了让子级Widget(如Text)使用</span></span>
<span class="line"><span style="color:#6A737D;">// Material Design 默认的样式风格,我们使用 Material 作为本路由的根。</span></span>
<span class="line"><span style="color:#79B8FF;">Material</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">  child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">CustomScrollView</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">    slivers</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">&lt;</span><span style="color:#79B8FF;">Widget</span><span style="color:#F97583;">&gt;</span><span style="color:#E1E4E8;">[</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#6A737D;">// AppBar，包含一个导航栏.</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#79B8FF;">SliverAppBar</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">        pinned</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">true</span><span style="color:#E1E4E8;">, </span><span style="color:#6A737D;">// 滑动到顶端时会固定住</span></span>
<span class="line"><span style="color:#E1E4E8;">        expandedHeight</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">250.0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">        flexibleSpace</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">FlexibleSpaceBar</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          title</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">const</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;Demo&#39;</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">          background</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Image</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">asset</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">            </span><span style="color:#9ECBFF;">&quot;./imgs/sea.png&quot;</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            fit</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">BoxFit</span><span style="color:#E1E4E8;">.cover,</span></span>
<span class="line"><span style="color:#E1E4E8;">          ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#79B8FF;">SliverPadding</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">        padding</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">const</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">EdgeInsets</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">all</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">8.0</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">        sliver</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverGrid</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          </span><span style="color:#6A737D;">//Grid</span></span>
<span class="line"><span style="color:#E1E4E8;">          gridDelegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverGridDelegateWithFixedCrossAxisCount</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">            crossAxisCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">2</span><span style="color:#E1E4E8;">, </span><span style="color:#6A737D;">//Grid按两列显示</span></span>
<span class="line"><span style="color:#E1E4E8;">            mainAxisSpacing</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">10.0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            crossAxisSpacing</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">10.0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            childAspectRatio</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">4.0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">          ),</span></span>
<span class="line"><span style="color:#E1E4E8;">          delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverChildBuilderDelegate</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">            (</span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context, </span><span style="color:#79B8FF;">int</span><span style="color:#E1E4E8;"> index) {</span></span>
<span class="line"><span style="color:#E1E4E8;">              </span><span style="color:#6A737D;">//创建子widget</span></span>
<span class="line"><span style="color:#E1E4E8;">              </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Container</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">                alignment</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Alignment</span><span style="color:#E1E4E8;">.center,</span></span>
<span class="line"><span style="color:#E1E4E8;">                color</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Colors</span><span style="color:#E1E4E8;">.cyan[</span><span style="color:#79B8FF;">100</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">*</span><span style="color:#E1E4E8;"> (index </span><span style="color:#F97583;">%</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">9</span><span style="color:#E1E4E8;">)],</span></span>
<span class="line"><span style="color:#E1E4E8;">                child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;grid item $</span><span style="color:#79B8FF;">index</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">              );</span></span>
<span class="line"><span style="color:#E1E4E8;">            },</span></span>
<span class="line"><span style="color:#E1E4E8;">            childCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">20</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">          ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#79B8FF;">SliverFixedExtentList</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">        itemExtent</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">50.0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">        delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverChildBuilderDelegate</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          (</span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context, </span><span style="color:#79B8FF;">int</span><span style="color:#E1E4E8;"> index) {</span></span>
<span class="line"><span style="color:#E1E4E8;">            </span><span style="color:#6A737D;">//创建列表项</span></span>
<span class="line"><span style="color:#E1E4E8;">            </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Container</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">              alignment</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Alignment</span><span style="color:#E1E4E8;">.center,</span></span>
<span class="line"><span style="color:#E1E4E8;">              color</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Colors</span><span style="color:#E1E4E8;">.lightBlue[</span><span style="color:#79B8FF;">100</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">*</span><span style="color:#E1E4E8;"> (index </span><span style="color:#F97583;">%</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">9</span><span style="color:#E1E4E8;">)],</span></span>
<span class="line"><span style="color:#E1E4E8;">              child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;list item $</span><span style="color:#79B8FF;">index</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">            );</span></span>
<span class="line"><span style="color:#E1E4E8;">          },</span></span>
<span class="line"><span style="color:#E1E4E8;">          childCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">20</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ),</span></span>
<span class="line"><span style="color:#E1E4E8;">    ],</span></span>
<span class="line"><span style="color:#E1E4E8;">  ),</span></span>
<span class="line"><span style="color:#E1E4E8;">);</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#6A737D;">// 因为本路由没有使用 Scaffold，为了让子级Widget(如Text)使用</span></span>
<span class="line"><span style="color:#6A737D;">// Material Design 默认的样式风格,我们使用 Material 作为本路由的根。</span></span>
<span class="line"><span style="color:#005CC5;">Material</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">  child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">CustomScrollView</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">    slivers</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">&lt;</span><span style="color:#005CC5;">Widget</span><span style="color:#D73A49;">&gt;</span><span style="color:#24292E;">[</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#6A737D;">// AppBar，包含一个导航栏.</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#005CC5;">SliverAppBar</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">        pinned</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">true</span><span style="color:#24292E;">, </span><span style="color:#6A737D;">// 滑动到顶端时会固定住</span></span>
<span class="line"><span style="color:#24292E;">        expandedHeight</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">250.0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">        flexibleSpace</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">FlexibleSpaceBar</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          title</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">const</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;Demo&#39;</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">          background</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Image</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">asset</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">            </span><span style="color:#032F62;">&quot;./imgs/sea.png&quot;</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            fit</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">BoxFit</span><span style="color:#24292E;">.cover,</span></span>
<span class="line"><span style="color:#24292E;">          ),</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">      ),</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#005CC5;">SliverPadding</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">        padding</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">const</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">EdgeInsets</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">all</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">8.0</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">        sliver</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverGrid</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          </span><span style="color:#6A737D;">//Grid</span></span>
<span class="line"><span style="color:#24292E;">          gridDelegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverGridDelegateWithFixedCrossAxisCount</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">            crossAxisCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">2</span><span style="color:#24292E;">, </span><span style="color:#6A737D;">//Grid按两列显示</span></span>
<span class="line"><span style="color:#24292E;">            mainAxisSpacing</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">10.0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            crossAxisSpacing</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">10.0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            childAspectRatio</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">4.0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">          ),</span></span>
<span class="line"><span style="color:#24292E;">          delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverChildBuilderDelegate</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">            (</span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context, </span><span style="color:#005CC5;">int</span><span style="color:#24292E;"> index) {</span></span>
<span class="line"><span style="color:#24292E;">              </span><span style="color:#6A737D;">//创建子widget</span></span>
<span class="line"><span style="color:#24292E;">              </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Container</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">                alignment</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Alignment</span><span style="color:#24292E;">.center,</span></span>
<span class="line"><span style="color:#24292E;">                color</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Colors</span><span style="color:#24292E;">.cyan[</span><span style="color:#005CC5;">100</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">*</span><span style="color:#24292E;"> (index </span><span style="color:#D73A49;">%</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">9</span><span style="color:#24292E;">)],</span></span>
<span class="line"><span style="color:#24292E;">                child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;grid item $</span><span style="color:#005CC5;">index</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">              );</span></span>
<span class="line"><span style="color:#24292E;">            },</span></span>
<span class="line"><span style="color:#24292E;">            childCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">20</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">          ),</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">      ),</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#005CC5;">SliverFixedExtentList</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">        itemExtent</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">50.0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">        delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverChildBuilderDelegate</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          (</span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context, </span><span style="color:#005CC5;">int</span><span style="color:#24292E;"> index) {</span></span>
<span class="line"><span style="color:#24292E;">            </span><span style="color:#6A737D;">//创建列表项</span></span>
<span class="line"><span style="color:#24292E;">            </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Container</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">              alignment</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Alignment</span><span style="color:#24292E;">.center,</span></span>
<span class="line"><span style="color:#24292E;">              color</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Colors</span><span style="color:#24292E;">.lightBlue[</span><span style="color:#005CC5;">100</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">*</span><span style="color:#24292E;"> (index </span><span style="color:#D73A49;">%</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">9</span><span style="color:#24292E;">)],</span></span>
<span class="line"><span style="color:#24292E;">              child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;list item $</span><span style="color:#005CC5;">index</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">            );</span></span>
<span class="line"><span style="color:#24292E;">          },</span></span>
<span class="line"><span style="color:#24292E;">          childCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">20</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">      ),</span></span>
<span class="line"><span style="color:#24292E;">    ],</span></span>
<span class="line"><span style="color:#24292E;">  ),</span></span>
<span class="line"><span style="color:#24292E;">);</span></span></code></pre></div><p>代码分为三部分：</p><ul><li>头部<code>SliverAppBar</code>：<code>SliverAppBar</code>对应<code>AppBar</code>，两者不同之处在于<code>SliverAppBar</code>可以集成到<code>CustomScrollView</code>。<code>SliverAppBar</code>可以结合<code>FlexibleSpaceBar</code>实现Material Design中头部伸缩的模型，具体效果，读者可以运行该示例查看。</li><li>中间的<code>SliverGrid</code>：它用<code>SliverPadding</code>包裹以给<code>SliverGrid</code>添加补白。<code>SliverGrid</code>是一个两列，宽高比为4的网格，它有20个子组件。</li><li>底部<code>SliverFixedExtentList</code>：它是一个所有子元素高度都为50像素的列表。</li></ul><p>运行效果如图6-25、6-26所示：</p><p><img src="/assets/6-25.81e6a770.png" alt="图6-25"><img src="/assets/6-26.081578bc.png" alt="图6-26"></p><h3 id="slivertoboxadapter" tabindex="-1">SliverToBoxAdapter <a class="header-anchor" href="#slivertoboxadapter" aria-label="Permalink to &quot;SliverToBoxAdapter&quot;">​</a></h3><p>在实际布局中，我们通常需要往 CustomScrollView 中添加一些自定义的组件，而这些组件并非都有 Sliver 版本，为此 Flutter 提供了一个 SliverToBoxAdapter 组件，它是一个适配器：可以将 RenderBox 适配为 Sliver。比如我们想在列表顶部添加一个可以横向滑动的 PageView，可以使用 SliverToBoxAdapter 来配置：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#79B8FF;">CustomScrollView</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">  slivers</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> [</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">SliverToBoxAdapter</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SizedBox</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">        height</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">300</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">        child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">PageView</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          children</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> [</span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&quot;1&quot;</span><span style="color:#E1E4E8;">), </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&quot;2&quot;</span><span style="color:#E1E4E8;">)],</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ),</span></span>
<span class="line"><span style="color:#E1E4E8;">    ),</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#B392F0;">buildSliverFixedList</span><span style="color:#E1E4E8;">(),</span></span>
<span class="line"><span style="color:#E1E4E8;">  ],</span></span>
<span class="line"><span style="color:#E1E4E8;">);</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#005CC5;">CustomScrollView</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">  slivers</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> [</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">SliverToBoxAdapter</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SizedBox</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">        height</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">300</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">        child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">PageView</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          children</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> [</span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&quot;1&quot;</span><span style="color:#24292E;">), </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&quot;2&quot;</span><span style="color:#24292E;">)],</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">      ),</span></span>
<span class="line"><span style="color:#24292E;">    ),</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#6F42C1;">buildSliverFixedList</span><span style="color:#24292E;">(),</span></span>
<span class="line"><span style="color:#24292E;">  ],</span></span>
<span class="line"><span style="color:#24292E;">);</span></span></code></pre></div><p>注意，上面的代码是可以正常运行的，但是如果将 PageView 换成一个滑动方向和 CustomScrollView 一致的 ListView 则不会正常工作！原因是：CustomScrollView 组合 Sliver 的原理是为所有子 Sliver 提供一个共享的 Scrollable，然后统一处理指定滑动方向的滑动事件，如果 Sliver 中引入了其他的 Scrollable，则滑动事件便会冲突。上例中 PageView 之所以能正常工作，是因为 PageView 的 Scrollable 只处理水平方向的滑动，而 CustomScrollView 是处理垂直方向的，两者并未冲突，所以不会有问题，但是换一个也是垂直方向的 ListView 时则不能正常工作，最终的效果是，在ListView内滑动时只会对ListView 起作用，原因是滑动事件被 ListView 的 Scrollable 优先消费，CustomScrollView 的 Scrollable 便接收不到滑动事件了。</p><blockquote><p>Flutter 中手势的冲突时，默认的策略是子元素生效，这个我们将在后面事件处理相关章节介绍。</p></blockquote><p>所以我们可以得出一个结论：<strong>如果 CustomScrollView 有孩子也是一个完整的可滚动组件且它们的滑动方向一致，则 CustomScrollView 不能正常工作</strong>。要解决这个问题，可以使用 NestedScrollView，这个我们将在下一节介绍。</p><h3 id="sliverpersistentheader" tabindex="-1">SliverPersistentHeader <a class="header-anchor" href="#sliverpersistentheader" aria-label="Permalink to &quot;SliverPersistentHeader&quot;">​</a></h3><p>SliverPersistentHeader 的功能是当滑动到 CustomScrollView 的顶部时，可以将组件固定在顶部。</p><p>需要注意， Flutter 中设计 SliverPersistentHeader 组件的初衷是为了实现 SliverAppBar，所以它的一些属性和回调在SliverAppBar 中才会用到。因此，如果我们要直接使用 SliverPersistentHeader，看到它的一些配置和参数会感到疑惑，使用起来会感觉有心智成本，为此，笔者会在下面介绍中指出哪些是需要我们重点关注的，哪些是可以忽略的，最后为了便于使用，我们会封装一个<code>SliverHeaderDelegate</code> ，通过它我们只需要配置我们关注的属性即可。</p><p>我们先看看 SliverPersistentHeader 的定义：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#F97583;">const</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverPersistentHeader</span><span style="color:#E1E4E8;">({</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Key</span><span style="color:#F97583;">?</span><span style="color:#E1E4E8;"> key,</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 构造 header 组件的委托</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverPersistentHeaderDelegate</span><span style="color:#E1E4E8;"> delegate,</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.pinned </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">false</span><span style="color:#E1E4E8;">, </span><span style="color:#6A737D;">// header 滑动到可视区域顶部时是否固定在顶部</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.floating </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">false</span><span style="color:#E1E4E8;">, </span><span style="color:#6A737D;">// 正文部分介绍</span></span>
<span class="line"><span style="color:#E1E4E8;">})</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#D73A49;">const</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverPersistentHeader</span><span style="color:#24292E;">({</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Key</span><span style="color:#D73A49;">?</span><span style="color:#24292E;"> key,</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 构造 header 组件的委托</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverPersistentHeaderDelegate</span><span style="color:#24292E;"> delegate,</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.pinned </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">false</span><span style="color:#24292E;">, </span><span style="color:#6A737D;">// header 滑动到可视区域顶部时是否固定在顶部</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.floating </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">false</span><span style="color:#24292E;">, </span><span style="color:#6A737D;">// 正文部分介绍</span></span>
<span class="line"><span style="color:#24292E;">})</span></span></code></pre></div><p><code>floating</code> 的作用是：<code>pinned</code> 为 false 时 ，则 header 可以滑出可视区域（CustomScrollView 的 Viewport）（不会固定到顶部），当用户再次向下滑动时，此时不管 header 已经被滑出了多远，它都会立即出现在可视区域顶部并固定住，直到继续下滑到 header 在列表中原来的位置时，header 才会重新回到原来的位置（不再固定在顶部）。 具体效果，我们后面会有示例，读者可以实际运行起来看看效果。</p><p><code>delegate</code> 是用于生成 header 的委托，类型为 SliverPersistentHeaderDelegate，它是一个抽象类，需要我们自己实现，定义如下：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#F97583;">abstract</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">class</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverPersistentHeaderDelegate</span><span style="color:#E1E4E8;"> {</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// header 最大高度；pined为 true 时，当 header 刚刚固定到顶部时高度为最大高度。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> maxExtent;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// header 的最小高度；pined为true时，当header固定到顶部，用户继续往上滑动时，header</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 的高度会随着用户继续上滑从 maxExtent 逐渐减小到 minExtent</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> minExtent;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 构建 header。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// shrinkOffset取值范围[0,maxExtent],当header刚刚到达顶部时，shrinkOffset 值为0，</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 如果用户继续向上滑动列表，shrinkOffset的值会随着用户滑动的偏移减小，直到减到0时。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">//</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// overlapsContent：一般不建议使用，在使用时一定要小心，后面会解释。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">build</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context, </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> shrinkOffset, </span><span style="color:#79B8FF;">bool</span><span style="color:#E1E4E8;"> overlapsContent);</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// header 是否需要重新构建；通常当父级的 StatefulWidget 更新状态时会触发。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 一般来说只有当 Delegate 的配置发生变化时，应该返回false，比如新旧的 minExtent、maxExtent</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 等其他配置不同时需要返回 true，其余情况返回 false 即可。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">bool</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">shouldRebuild</span><span style="color:#E1E4E8;">(</span><span style="color:#F97583;">covariant</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverPersistentHeaderDelegate</span><span style="color:#E1E4E8;"> oldDelegate);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 下面这几个属性是SliverPersistentHeader在SliverAppBar中时实现floating、snap </span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 效果时会用到，平时开发过程很少使用到，读者可以先不用理会。</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">TickerProvider</span><span style="color:#F97583;">?</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> vsync </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">null</span><span style="color:#E1E4E8;">;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">FloatingHeaderSnapConfiguration</span><span style="color:#F97583;">?</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> snapConfiguration </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">null</span><span style="color:#E1E4E8;">;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">OverScrollHeaderStretchConfiguration</span><span style="color:#F97583;">?</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> stretchConfiguration </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">null</span><span style="color:#E1E4E8;">;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">PersistentHeaderShowOnScreenConfiguration</span><span style="color:#F97583;">?</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> showOnScreenConfiguration </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">null</span><span style="color:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">}</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#D73A49;">abstract</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">class</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverPersistentHeaderDelegate</span><span style="color:#24292E;"> {</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// header 最大高度；pined为 true 时，当 header 刚刚固定到顶部时高度为最大高度。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> maxExtent;</span></span>
<span class="line"><span style="color:#24292E;">  </span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// header 的最小高度；pined为true时，当header固定到顶部，用户继续往上滑动时，header</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 的高度会随着用户继续上滑从 maxExtent 逐渐减小到 minExtent</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> minExtent;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 构建 header。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// shrinkOffset取值范围[0,maxExtent],当header刚刚到达顶部时，shrinkOffset 值为0，</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 如果用户继续向上滑动列表，shrinkOffset的值会随着用户滑动的偏移减小，直到减到0时。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">//</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// overlapsContent：一般不建议使用，在使用时一定要小心，后面会解释。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">build</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context, </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> shrinkOffset, </span><span style="color:#005CC5;">bool</span><span style="color:#24292E;"> overlapsContent);</span></span>
<span class="line"><span style="color:#24292E;">  </span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// header 是否需要重新构建；通常当父级的 StatefulWidget 更新状态时会触发。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 一般来说只有当 Delegate 的配置发生变化时，应该返回false，比如新旧的 minExtent、maxExtent</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 等其他配置不同时需要返回 true，其余情况返回 false 即可。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">bool</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">shouldRebuild</span><span style="color:#24292E;">(</span><span style="color:#D73A49;">covariant</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverPersistentHeaderDelegate</span><span style="color:#24292E;"> oldDelegate);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 下面这几个属性是SliverPersistentHeader在SliverAppBar中时实现floating、snap </span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 效果时会用到，平时开发过程很少使用到，读者可以先不用理会。</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">TickerProvider</span><span style="color:#D73A49;">?</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> vsync </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">null</span><span style="color:#24292E;">;</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">FloatingHeaderSnapConfiguration</span><span style="color:#D73A49;">?</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> snapConfiguration </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">null</span><span style="color:#24292E;">;</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">OverScrollHeaderStretchConfiguration</span><span style="color:#D73A49;">?</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> stretchConfiguration </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">null</span><span style="color:#24292E;">;</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">PersistentHeaderShowOnScreenConfiguration</span><span style="color:#D73A49;">?</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> showOnScreenConfiguration </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">null</span><span style="color:#24292E;">;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">}</span></span></code></pre></div><p>可以看到，我们最需要关注的就是<code>maxExtent</code> 和 <code>minExtent</code>；<code>pined </code>为<code>true</code> 时，当 header 刚刚固定到顶部，此时会对它应用 <code>maxExtent</code> （最大高度）；当用户继续往上滑动时，header 的高度会随着用户继续上滑从 <code>maxExtent</code> 逐渐减小到 <code>minExtent</code>。如果我们想让 header 高度固定，则将 <code>maxExtent</code> 和 <code>minExtent</code> 指定为同样的值即可。</p><p>为了构建 header 我们必须要定义一个类，让它继承自 SliverPersistentHeaderDelegate，这无疑会增加使用成本！为此，我们封装一个通用的委托构造器 SliverHeaderDelegate，通过它可以快速构建 SliverPersistentHeaderDelegate，实现如下：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#F97583;">typedef</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverHeaderBuilder</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Function</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context, </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> shrinkOffset, </span><span style="color:#79B8FF;">bool</span><span style="color:#E1E4E8;"> overlapsContent);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#F97583;">class</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">extends</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverPersistentHeaderDelegate</span><span style="color:#E1E4E8;"> {</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// child 为 header</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;">({</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.maxHeight,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.minHeight </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> child,</span></span>
<span class="line"><span style="color:#E1E4E8;">  })  </span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> builder </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> ((a, b, c) </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> child),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#F97583;">assert</span><span style="color:#E1E4E8;">(minHeight </span><span style="color:#F97583;">&lt;=</span><span style="color:#E1E4E8;"> maxHeight </span><span style="color:#F97583;">&amp;&amp;</span><span style="color:#E1E4E8;"> minHeight </span><span style="color:#F97583;">&gt;=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">0</span><span style="color:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">//最大和最小高度相同</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">fixedHeight</span><span style="color:#E1E4E8;">({</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> height,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> child,</span></span>
<span class="line"><span style="color:#E1E4E8;">  })  </span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> builder </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> ((a, b, c) </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> child),</span></span>
<span class="line"><span style="color:#E1E4E8;">        maxHeight </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> height,</span></span>
<span class="line"><span style="color:#E1E4E8;">        minHeight </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> height;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">//需要自定义builder时使用</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">builder</span><span style="color:#E1E4E8;">({</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.maxHeight,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.minHeight </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">0</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">required</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">this</span><span style="color:#E1E4E8;">.builder,</span></span>
<span class="line"><span style="color:#E1E4E8;">  });</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">final</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> maxHeight;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">final</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> minHeight;</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">final</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverHeaderBuilder</span><span style="color:#E1E4E8;"> builder;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">@override</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">build</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> shrinkOffset,</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">bool</span><span style="color:#E1E4E8;"> overlapsContent,</span></span>
<span class="line"><span style="color:#E1E4E8;">  ) {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> child </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">builder</span><span style="color:#E1E4E8;">(context, shrinkOffset, overlapsContent);</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#6A737D;">//测试代码：如果在调试模式，且子组件设置了key，则打印日志</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">assert</span><span style="color:#E1E4E8;">(() {</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#F97583;">if</span><span style="color:#E1E4E8;"> (child.key </span><span style="color:#F97583;">!=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">null</span><span style="color:#E1E4E8;">) {</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#B392F0;">print</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;${</span><span style="color:#79B8FF;">child</span><span style="color:#9ECBFF;">.</span><span style="color:#79B8FF;">key</span><span style="color:#9ECBFF;">}: shrink: $</span><span style="color:#79B8FF;">shrinkOffset</span><span style="color:#9ECBFF;">，overlaps:$</span><span style="color:#79B8FF;">overlapsContent</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">);</span></span>
<span class="line"><span style="color:#E1E4E8;">      }</span></span>
<span class="line"><span style="color:#E1E4E8;">      </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">true</span><span style="color:#E1E4E8;">;</span></span>
<span class="line"><span style="color:#E1E4E8;">    }());</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#6A737D;">// 让 header 尽可能充满限制的空间；宽度为 Viewport 宽度，</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#6A737D;">// 高度随着用户滑动在[minHeight,maxHeight]之间变化。</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SizedBox</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">expand</span><span style="color:#E1E4E8;">(child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> child);</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">@override</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> maxExtent </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> maxHeight;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">@override</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">double</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">get</span><span style="color:#E1E4E8;"> minExtent </span><span style="color:#F97583;">=&gt;</span><span style="color:#E1E4E8;"> minHeight;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">@override</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">bool</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">shouldRebuild</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;"> old) {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> old.maxExtent </span><span style="color:#F97583;">!=</span><span style="color:#E1E4E8;"> maxExtent </span><span style="color:#F97583;">||</span><span style="color:#E1E4E8;"> old.minExtent </span><span style="color:#F97583;">!=</span><span style="color:#E1E4E8;"> minExtent;</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"><span style="color:#E1E4E8;">}</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#D73A49;">typedef</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverHeaderBuilder</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Function</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context, </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> shrinkOffset, </span><span style="color:#005CC5;">bool</span><span style="color:#24292E;"> overlapsContent);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#D73A49;">class</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">extends</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverPersistentHeaderDelegate</span><span style="color:#24292E;"> {</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// child 为 header</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;">({</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.maxHeight,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.minHeight </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> child,</span></span>
<span class="line"><span style="color:#24292E;">  })  </span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> builder </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> ((a, b, c) </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> child),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#D73A49;">assert</span><span style="color:#24292E;">(minHeight </span><span style="color:#D73A49;">&lt;=</span><span style="color:#24292E;"> maxHeight </span><span style="color:#D73A49;">&amp;&amp;</span><span style="color:#24292E;"> minHeight </span><span style="color:#D73A49;">&gt;=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">0</span><span style="color:#24292E;">);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">//最大和最小高度相同</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">fixedHeight</span><span style="color:#24292E;">({</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> height,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> child,</span></span>
<span class="line"><span style="color:#24292E;">  })  </span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> builder </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> ((a, b, c) </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> child),</span></span>
<span class="line"><span style="color:#24292E;">        maxHeight </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> height,</span></span>
<span class="line"><span style="color:#24292E;">        minHeight </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> height;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">//需要自定义builder时使用</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">builder</span><span style="color:#24292E;">({</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.maxHeight,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.minHeight </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">0</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">required</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">this</span><span style="color:#24292E;">.builder,</span></span>
<span class="line"><span style="color:#24292E;">  });</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">final</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> maxHeight;</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">final</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> minHeight;</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">final</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverHeaderBuilder</span><span style="color:#24292E;"> builder;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">@override</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">build</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> shrinkOffset,</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">bool</span><span style="color:#24292E;"> overlapsContent,</span></span>
<span class="line"><span style="color:#24292E;">  ) {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> child </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">builder</span><span style="color:#24292E;">(context, shrinkOffset, overlapsContent);</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#6A737D;">//测试代码：如果在调试模式，且子组件设置了key，则打印日志</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">assert</span><span style="color:#24292E;">(() {</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#D73A49;">if</span><span style="color:#24292E;"> (child.key </span><span style="color:#D73A49;">!=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">null</span><span style="color:#24292E;">) {</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#6F42C1;">print</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;${</span><span style="color:#005CC5;">child</span><span style="color:#032F62;">.</span><span style="color:#005CC5;">key</span><span style="color:#032F62;">}: shrink: $</span><span style="color:#005CC5;">shrinkOffset</span><span style="color:#032F62;">，overlaps:$</span><span style="color:#005CC5;">overlapsContent</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">);</span></span>
<span class="line"><span style="color:#24292E;">      }</span></span>
<span class="line"><span style="color:#24292E;">      </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">true</span><span style="color:#24292E;">;</span></span>
<span class="line"><span style="color:#24292E;">    }());</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#6A737D;">// 让 header 尽可能充满限制的空间；宽度为 Viewport 宽度，</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#6A737D;">// 高度随着用户滑动在[minHeight,maxHeight]之间变化。</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SizedBox</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">expand</span><span style="color:#24292E;">(child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> child);</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">@override</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> maxExtent </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> maxHeight;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">@override</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">double</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">get</span><span style="color:#24292E;"> minExtent </span><span style="color:#D73A49;">=&gt;</span><span style="color:#24292E;"> minHeight;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">@override</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">bool</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">shouldRebuild</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;"> old) {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> old.maxExtent </span><span style="color:#D73A49;">!=</span><span style="color:#24292E;"> maxExtent </span><span style="color:#D73A49;">||</span><span style="color:#24292E;"> old.minExtent </span><span style="color:#D73A49;">!=</span><span style="color:#24292E;"> minExtent;</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"><span style="color:#24292E;">}</span></span></code></pre></div><p>实现很简单，不再赘述，下面我们看看如何使用：</p><div class="language-dart vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">dart</span><pre class="shiki github-dark vp-code-dark"><code><span class="line"><span style="color:#F97583;">class</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">PersistentHeaderRoute</span><span style="color:#E1E4E8;"> </span><span style="color:#F97583;">extends</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">StatelessWidget</span><span style="color:#E1E4E8;"> {</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#F97583;">@override</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">build</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">BuildContext</span><span style="color:#E1E4E8;"> context) {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">CustomScrollView</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      slivers</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> [</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#B392F0;">buildSliverList</span><span style="color:#E1E4E8;">(),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#79B8FF;">SliverPersistentHeader</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          pinned</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">true</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">          delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;">(</span><span style="color:#6A737D;">//有最大和最小高度</span></span>
<span class="line"><span style="color:#E1E4E8;">            maxHeight</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">80</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            minHeight</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">50</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildHeader</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">1</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">          ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#B392F0;">buildSliverList</span><span style="color:#E1E4E8;">(),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#79B8FF;">SliverPersistentHeader</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">          pinned</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">true</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">          delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverHeaderDelegate</span><span style="color:#E1E4E8;">.</span><span style="color:#B392F0;">fixedHeight</span><span style="color:#E1E4E8;">( </span><span style="color:#6A737D;">//固定高度</span></span>
<span class="line"><span style="color:#E1E4E8;">            height</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">50</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">            child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildHeader</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">2</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">          ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        ),</span></span>
<span class="line"><span style="color:#E1E4E8;">        </span><span style="color:#B392F0;">buildSliverList</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">20</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">      ],</span></span>
<span class="line"><span style="color:#E1E4E8;">    );</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 构建固定高度的SliverList，count为列表项属相</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildSliverList</span><span style="color:#E1E4E8;">([</span><span style="color:#79B8FF;">int</span><span style="color:#E1E4E8;"> count </span><span style="color:#F97583;">=</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">5</span><span style="color:#E1E4E8;">]) {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverFixedExtentList</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      itemExtent</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">50</span><span style="color:#E1E4E8;">,</span></span>
<span class="line"><span style="color:#E1E4E8;">      delegate</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">SliverChildBuilderDelegate</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">        (context, index) {</span></span>
<span class="line"><span style="color:#E1E4E8;">          </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">ListTile</span><span style="color:#E1E4E8;">(title</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&#39;$</span><span style="color:#79B8FF;">index</span><span style="color:#9ECBFF;">&#39;</span><span style="color:#E1E4E8;">));</span></span>
<span class="line"><span style="color:#E1E4E8;">        },</span></span>
<span class="line"><span style="color:#E1E4E8;">        childCount</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> count,</span></span>
<span class="line"><span style="color:#E1E4E8;">      ),</span></span>
<span class="line"><span style="color:#E1E4E8;">    );</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#6A737D;">// 构建 header</span></span>
<span class="line"><span style="color:#E1E4E8;">  </span><span style="color:#79B8FF;">Widget</span><span style="color:#E1E4E8;"> </span><span style="color:#B392F0;">buildHeader</span><span style="color:#E1E4E8;">(</span><span style="color:#79B8FF;">int</span><span style="color:#E1E4E8;"> i) {</span></span>
<span class="line"><span style="color:#E1E4E8;">    </span><span style="color:#F97583;">return</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Container</span><span style="color:#E1E4E8;">(</span></span>
<span class="line"><span style="color:#E1E4E8;">      color</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Colors</span><span style="color:#E1E4E8;">.lightBlue.shade200,</span></span>
<span class="line"><span style="color:#E1E4E8;">      alignment</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Alignment</span><span style="color:#E1E4E8;">.centerLeft,</span></span>
<span class="line"><span style="color:#E1E4E8;">      child</span><span style="color:#F97583;">:</span><span style="color:#E1E4E8;"> </span><span style="color:#79B8FF;">Text</span><span style="color:#E1E4E8;">(</span><span style="color:#9ECBFF;">&quot;PersistentHeader $</span><span style="color:#79B8FF;">i</span><span style="color:#9ECBFF;">&quot;</span><span style="color:#E1E4E8;">),</span></span>
<span class="line"><span style="color:#E1E4E8;">    );</span></span>
<span class="line"><span style="color:#E1E4E8;">  }</span></span>
<span class="line"><span style="color:#E1E4E8;">}</span></span></code></pre><pre class="shiki github-light vp-code-light"><code><span class="line"><span style="color:#D73A49;">class</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">PersistentHeaderRoute</span><span style="color:#24292E;"> </span><span style="color:#D73A49;">extends</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">StatelessWidget</span><span style="color:#24292E;"> {</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#D73A49;">@override</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">build</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">BuildContext</span><span style="color:#24292E;"> context) {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">CustomScrollView</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      slivers</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> [</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#6F42C1;">buildSliverList</span><span style="color:#24292E;">(),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#005CC5;">SliverPersistentHeader</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          pinned</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">true</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">          delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;">(</span><span style="color:#6A737D;">//有最大和最小高度</span></span>
<span class="line"><span style="color:#24292E;">            maxHeight</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">80</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            minHeight</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">50</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildHeader</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">1</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">          ),</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#6F42C1;">buildSliverList</span><span style="color:#24292E;">(),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#005CC5;">SliverPersistentHeader</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">          pinned</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">true</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">          delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverHeaderDelegate</span><span style="color:#24292E;">.</span><span style="color:#6F42C1;">fixedHeight</span><span style="color:#24292E;">( </span><span style="color:#6A737D;">//固定高度</span></span>
<span class="line"><span style="color:#24292E;">            height</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">50</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">            child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildHeader</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">2</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">          ),</span></span>
<span class="line"><span style="color:#24292E;">        ),</span></span>
<span class="line"><span style="color:#24292E;">        </span><span style="color:#6F42C1;">buildSliverList</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">20</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">      ],</span></span>
<span class="line"><span style="color:#24292E;">    );</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 构建固定高度的SliverList，count为列表项属相</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildSliverList</span><span style="color:#24292E;">([</span><span style="color:#005CC5;">int</span><span style="color:#24292E;"> count </span><span style="color:#D73A49;">=</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">5</span><span style="color:#24292E;">]) {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverFixedExtentList</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      itemExtent</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">50</span><span style="color:#24292E;">,</span></span>
<span class="line"><span style="color:#24292E;">      delegate</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">SliverChildBuilderDelegate</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">        (context, index) {</span></span>
<span class="line"><span style="color:#24292E;">          </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">ListTile</span><span style="color:#24292E;">(title</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&#39;$</span><span style="color:#005CC5;">index</span><span style="color:#032F62;">&#39;</span><span style="color:#24292E;">));</span></span>
<span class="line"><span style="color:#24292E;">        },</span></span>
<span class="line"><span style="color:#24292E;">        childCount</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> count,</span></span>
<span class="line"><span style="color:#24292E;">      ),</span></span>
<span class="line"><span style="color:#24292E;">    );</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#6A737D;">// 构建 header</span></span>
<span class="line"><span style="color:#24292E;">  </span><span style="color:#005CC5;">Widget</span><span style="color:#24292E;"> </span><span style="color:#6F42C1;">buildHeader</span><span style="color:#24292E;">(</span><span style="color:#005CC5;">int</span><span style="color:#24292E;"> i) {</span></span>
<span class="line"><span style="color:#24292E;">    </span><span style="color:#D73A49;">return</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Container</span><span style="color:#24292E;">(</span></span>
<span class="line"><span style="color:#24292E;">      color</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Colors</span><span style="color:#24292E;">.lightBlue.shade200,</span></span>
<span class="line"><span style="color:#24292E;">      alignment</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Alignment</span><span style="color:#24292E;">.centerLeft,</span></span>
<span class="line"><span style="color:#24292E;">      child</span><span style="color:#D73A49;">:</span><span style="color:#24292E;"> </span><span style="color:#005CC5;">Text</span><span style="color:#24292E;">(</span><span style="color:#032F62;">&quot;PersistentHeader $</span><span style="color:#005CC5;">i</span><span style="color:#032F62;">&quot;</span><span style="color:#24292E;">),</span></span>
<span class="line"><span style="color:#24292E;">    );</span></span>
<span class="line"><span style="color:#24292E;">  }</span></span>
<span class="line"><span style="color:#24292E;">}</span></span></code></pre></div><p>运行后效果如图6-27所示:</p><p><img src="/assets/6-27.b03009ba.gif" alt="图6-27"></p><h4 id="一些注意点" tabindex="-1">一些注意点 <a class="header-anchor" href="#一些注意点" aria-label="Permalink to &quot;一些注意点&quot;">​</a></h4><p>我们说过 SliverPersistentHeader 的 builder 参数 overlapsContent 一般不建议使用，使用时要当心。因为按照 overlapsContent 变量名的字面意思，只要有内容和 Sliver 重叠时就应该为 true，但是如果我们在上面示例的 builder 中打印一下 overlapsContent 的值就会发现第一个 PersistentHeader 1 的 overlapsContent 值一直都是 false，而 PersistentHeader 2 则是正常的，如果我们再添加几个 SliverPersistentHeader ，发现新添加的也都正常。总结一下：<strong>当有多个 SliverPersistentHeader时，需要注意第一个 SliverPersistentHeader 的 overlapsContent 值会一直为 false</strong>。</p><p>这可能是一个 bug，也可能就是这么设计的，因为 SliverPersistentHeader 的设计初衷主要是为了实现 SliverAppBar，可能并没有考虑到通用的场景，但是不管怎样，当前的 flutter 版本（2.5）中表现就是如此。为此，我们可以定一条约定：<strong>如果我们在使用 SliverPersistentHeader 构建子组件时需要依赖 overlapsContent 参数，则必须保证之前至少还有一个 SliverPersistentHeader 或 SliverAppBar</strong>（SliverAppBar 在当前 Flutter 版本的实现中内部包含了SliverPersistentHeader）。</p><h2 id="_6-10-3-总结" tabindex="-1">6.10.3 总结 <a class="header-anchor" href="#_6-10-3-总结" aria-label="Permalink to &quot;6.10.3 总结&quot;">​</a></h2><p>本节主要介绍了Flutter中常用的 Sliver，以及组合它们的 CustomScrollView。再次提醒读者：</p><ol><li>CustomScrollView 组合 Sliver 的原理是为所有子 Sliver 提供一个共享的 Scrollable，然后统一处理指定滑动方向的滑动事件。</li><li>CustomScrollView 和 ListView、GridView、PageView 一样，都是<strong>完整</strong>的可滚动组件（同时拥有 Scrollable、Viewport、Sliver）。</li><li>CustomScrollView 只能组合 Sliver，如果有孩子也是一个<strong>完整</strong>的可滚动组件（通过 SliverToBoxAdapter 嵌入）且它们的滑动方向一致时便不能正常工作。</li></ol><p>下一节中我们将介绍如何通过 NestedScrollView 嵌套两个完整的可滚动组件。</p></div></div></main><footer class="VPDocFooter" data-v-6b87e69f data-v-ef5dee53><!--[--><!--]--><div class="edit-info" data-v-ef5dee53><div class="edit-link" data-v-ef5dee53><a class="VPLink link vp-external-link-icon no-icon edit-link-button" href="https://gitee.com/luoguangguang/note/tree/master/docs/largeFrontEnd/flutter/chapter6/custom_scrollview.md" target="_blank" rel="noreferrer" data-v-ef5dee53><!--[--><svg xmlns="http://www.w3.org/2000/svg" viewbox="0 0 24 24" class="edit-link-icon" aria-label="edit icon" data-v-ef5dee53><path d="M18,23H4c-1.7,0-3-1.3-3-3V6c0-1.7,1.3-3,3-3h7c0.6,0,1,0.4,1,1s-0.4,1-1,1H4C3.4,5,3,5.4,3,6v14c0,0.6,0.4,1,1,1h14c0.6,0,1-0.4,1-1v-7c0-0.6,0.4-1,1-1s1,0.4,1,1v7C21,21.7,19.7,23,18,23z"></path><path d="M8,17c-0.3,0-0.5-0.1-0.7-0.3C7,16.5,6.9,16.1,7,15.8l1-4c0-0.2,0.1-0.3,0.3-0.5l9.5-9.5c1.2-1.2,3.2-1.2,4.4,0c1.2,1.2,1.2,3.2,0,4.4l-9.5,9.5c-0.1,0.1-0.3,0.2-0.5,0.3l-4,1C8.2,17,8.1,17,8,17zM9.9,12.5l-0.5,2.1l2.1-0.5l9.3-9.3c0.4-0.4,0.4-1.1,0-1.6c-0.4-0.4-1.2-0.4-1.6,0l0,0L9.9,12.5z M18.5,2.5L18.5,2.5L18.5,2.5z"></path></svg> 在Gitee上参与编辑此页<!--]--></a></div><!----></div><nav class="prev-next" data-v-ef5dee53><div class="pager" data-v-ef5dee53><!----></div><div class="pager" data-v-ef5dee53><a class="pager-link next" href="./largeFrontEnd/flutter/chapter1/index.html" data-v-ef5dee53><span class="desc" data-v-ef5dee53>Next page</span><span class="title" data-v-ef5dee53>第一章 初识Flutter</span></a></div></nav></footer><!--[--><!--]--></div></div></div><!--[--><!--]--></div></div><footer class="VPFooter has-sidebar" data-v-1919c326 data-v-e03eb2e1><div class="container" data-v-e03eb2e1><p class="message" data-v-e03eb2e1>Released under the MIT License.</p><p class="copyright" data-v-e03eb2e1>Copyright © 2023-present LG of GZU</p></div></footer><!--[--><!--]--></div></div>
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